Mercury 150 efi keeps stalling after fast idle

[trigby]

Hello every one, I just purchaced a 1997 Mercury 150 EFI the motor starts and runs good it seems while at fast idle but when it comes out of fast idle it starts to run rough and seems like it's smoking more than it should,and will eventually die, then when i try to restart,it just spins over and over. after it sets there ,say 30 minutes or so it will start up and do the same thing over again unless i give it more throttle then it will stay running but still rough.when shifting,it slams into gear like no interupter switch. sometimes it has no throttle response for a few seconds then starts picking up but still missing bad then it will pick up and run great at W.O.T. but once you let off and come back to an idle it wont be long it will die. Could this be the stator causing this problem? any help would be appreciated greatly , Tim. Oh all cylinders have around 145 psi

 

[sschefer]

Re: Mercury 150 efi keeps stalling after fast idle

Where did you get the motor? Did the person that you bought it from say anything about work they had done on it. The reason I ask is because 145 is a little higher than normal and might indicate that some performance mods were done. It would be very rare to see a stock original 97 motor hit 145. If nothing was done then check the throttle position sensor and the MAP sensor. Either one of those can cause your symptoms. Faulty injectors can do it also but check the other items first. A set of cut heads slapped on a stock powerhead can also do that, not always but I've had it happen.

 

[CharlieB]

Re: Mercury 150 efi keeps stalling after fast idle

Spark test each cyl cranking using an adjustable spark tester set to 7/16 inch.

A weak or no spark on one side can cause hard starting and poor low speed running.

Further testing the ignition with a DVA meter following the simple directions found in the Ignition Troubleshooting Guide available for free download from a link on the Support page of CDIElectronics

 

[trigby]

Re: Mercury 150 efi keeps stalling after fast idle

Ok thank you guys, im not sure what all has been done to the powerhead ,I do see a sticker on the back that tells me its a replacement power head, yes one cylinder is puching 150 psi ,I did notice on #6 cylinder the fire was kinda orange looking , i will have to find someone to check the map and throttle position sensor.I started looking at the fuel was pretty clean i disassembled the VST tank and screen was clean ,had minor trash in the bowl,I hope it's something simple,lol.Thanks ,Tim